This article is intended for network security administrators who use advanced wireless security features.

Preamble

It is the first part of the Physical Layer Convergence Protocol/Procedure (PLCP) Protocol Data Unit (PDU). A header is the remaining part of the data packets and has more information identifying the modulation scheme, transmission rate, and length of time to transmit the whole data frame.

Long preamble

PLCP with long preamble is transmitted at 1 Mbps regardless of transmit rate of data frames.

Total long preamble transfer time is a constant at 192 usec.

Compatible with legacy IEEE* 802.11 systems running at 1 and 2 Mbps

Short preamble

PLCP with short preamble: Preamble is transmitted at 1 Mbps and header at 2 Mbps.

Total short preamble transfer time is a constant at 96 usec.

Not compatible with legacy IEEE 802.11 systems operating at 1 and 2 Mbps

What does all this mean?

Most access points (AP) and broadband Wi-Fi routers are configured for a long preamble or have a setting that automatically detects the preamble and adjusts accordingly. A majority of client Wi-Fi adapters should also be pre-configured in the same manner as a precautionary measure for networks that may still employ legacy devices. Changing the default setting is not recommended. If you need to change the setting, see your equipment manufacturer before taking action.